Automatic regulating system having a movable control element and a follow-up element



R. H. NISBET April 20, 1948.

AUTOMATIC REGULATING SYSTEM HAVING A MOVABLE CONTROL ELEMENT AND A FOLLOW-UP ELEMENT Filed Feb. 19, 1944 INVENTOR E. H. /V/s57 When the control member is moved relative to the I pick-off member, the effective opening of one of the ports 8 is reduced and at the same time the effective opening of the other port is increased.

Each of the ports 8 is in permanent communication with a relatively stationary chamber In and the two chambers I areconne'cted respectively with pipe lines I2 and I4.

that movement of the piston valve will be halted it will thus be realised that the extent of movement of the piston valve will therefore be governed by the pressure difference in the pipes I2 and I4. It is to be noted that the piston heads II2 are of sufficient width relatively to the crosssectional size of the pipes H4 and are so arranged withrelation thereto that in movements of the piston valve, pressure fluid will not find its way to the back of the piston heads H2, H2.

The pipe lines l2 and I4 are connected respectively by auxiliary pipe lines I6 and I8 to opposite end portions of a fluid-pressure motor device in 'the form of'a double acting bellows device 20.

A suction pipe 6 opens into the pick-off member 2 so that a continuous stream of airis'dr'awn through the pipe lines I2 and I4, The suction in The bellows device actuates a slidable plate or and connecting rod to a lug 28 on the pickthese two pipe lines is equal when the controlmember 4 is in the neutral position'relative to.

the pick-off member 2, that is, whenboth ports 8 are equally partly obscured. On movement off the control member so that one of theports 0 becomes obscured to a greater extent than the" other, the flow through one of these ports is reduced relatively to the other so that a difference of pressure occurs between the two pipe lines I2 and I4, the sense of this pressure difference being determined by the direction of rotation of the control member 4 relative to the pick-offjmember 2.

The pipe lines I2 and I4'may be connected di-' rectly to a pneumatic servo-motor adapted to move the power-operated part under control to a position which depends upon the difierence of pressure between the two pipe lines I2 and I4. In the arrangement shown, however, the pipe lines I2 and I4 lead to a diaphragm I00 controlling an unbalanced relay valve I02 which in turn controls the operation of a hydraulic servo-motor IOI adapted to'actuate the part under control (not shown). While the relay valve I02 may be of any known type arranged so that the hydraulic pressure difference actingonthe piston of the servo and therefore the displacement of the part under "control depends both for direction and magnitude upon "the difference of pressure between the pipe lines I2 and I4, the relay valve I02 may conveniently comprise a cylinder having end portions I04, I04 of reduced cross-sectional area. The piston valve itself comprises a stem I06 having three piston heads thereon. The central piston head I08,which is located in the larger central portion of the cylinder, co-operates with an exhaust pipe H0 leading to a reservoir of the hydraulic fluid. The remaining piston heads II2 are located respectively in the end portions I04 of the cylinder andeach co-operates with an inlet pipe Il4. Pipes I I6 leading to opposite sides of the servo-motor IOI lead from the central portion of the cylinder and have the central piston head I08located therebetween. In the operation of this relay valve with movement of the stem I06 to the right as shown in the drawing, pressure will be built up on the right hand side of theservo-motor, whilst the left hand side of the servo-motor will be opened to exhaust by reason of movement of the central piston head I08 to the right away from the exhaust pipe I I0. The pres-' sure fiuid in the space between the piston head I08 and the right hand piston head I I2 will however, by exerting pressure against the right hand face of the central piston head I08, eventually balance the force, in the opposite direction, exerted on the stem I00 bythe diaphragm I00 so off member 2. r

The movements of the pick-off member under the force applied by the bellows device are resisted by means of control springs 38. The

the springs 38 to apply a restoring torque proportional to the movement of the pick-off member.

The pick-off member is also coupled by means of a connecting rod 32 to the piston rod 34 of a double-acting dashpot device 36.

Secured to the exterior of the member 2 is a toothed sector 40 meshing with a pinion 42 secured to a shaft 44 upon which a light fly-wheel 46 is also secured.

As previously indicated, a primary supervising instrument in the form of a gyroscope (not shown) maintains the member 4 in a fixed angular position about an axis, so that angular displacement of the member relative to the aircraft constitutes a measure of the deviation of the craft from the set course or attitude. The servo-motor IN is arranged to actuate a suitable control surface (not shown) of the aircraft for the purpose of correcting the deviations from set course or attitude to which the member 4 is sensitive.

When the aircraft deviates from the set course or attitude, the resulting relative movement of the member 4 with respect to the pick-off member 2 upsets the balance between the two ports 8 so that a diiference of pressure occurs between the two pipe-lines l2 and I4. The relay valve I02 responds to this pressure-difference and causes the servo-motor toxactuate the control surface in the direction appropriate for correcting the deviation. 7 g

The difference of pressure which occurs between the two pipe-lines I2 and I4 also acts on the bellows device 20 so'that' a force is applied through the connecting rod 26 to cause a torque to be applied to the pick-off member about its axis and this torque causes the pick-off member to be moved in the direction appropriate to nullify the relative movementbetween the members 4 and 2 which initiated the control action of the system. The pick-off member 2 thus tends to maintainalignment with the primarycontrol member 4. V V

This restoring movement .of the member 2 is opposed by three counter-forces or. torques, namely, (i) that due to the reaction of the springs ,33, (ii). that due to the reaction of the dash-pot 3B, and (iii) that due to the inertia of the wheel 40. The member 2 must therefore adjust itself so that the pressure difference in the pipe lines 'I2 and I4 acting on the bellows device 20 produces a force just suflicienttocounter- 5 baIal ie the stress (1), f-(ii) and '(ii-i "As pre viously in d ate'd; the-movement of the poweropr tea part under "control is proportional tothe pressurediii'ereneein the pipe lines I 2 and 8 4-. It --roiicws therefore that the movement of the part under control is proportional at every instant to the algebraic sum of three forces one of which is proportionalto the amplitude of the repeat back movement Whilst the other two a repieperucn'al tothe andsecond-"time derival-titres thereof. Thusithe correcting action applied by the control s'urface will dependnot only upon the amplitude-of any deviation from set course or attitude, upon the rateof --c'hange of this deviation and 'al'so upon the rate at which thesaid rate of change is increasing or diminishat any instant, i. e., on the displacement on the first and second derivatives. of this displacement with respect to time.

It is well known that a-control system having a relationshipof this kind between deviations from set course or attitude and the correcting action of'the control surface is capable of providing sensitive and acourate control such as will markedly assist in eliminating hunting.

It is 'desirable, to achieve theb'est results, to arrange that the total force opposing the displacement of the pick-off member -2, during a displacement of "the maximum magnitude and occurring at the maximum 'rate and acceleration that are liable to occur in operation, should not-exceed the pressuredii-rerence that the pickoff can provide at small relative displacement of the gyroscopeand pick-off. For this purpose the tension' of the 'springse-B, the drag resistance of the dash-pot 36 and the inertiaof thefiy-wheel 45 are kept low and the pick-off is designed (the members 2 and 4 being of relatively large dimensions) to have a sharply rising output for an initialsmall relative displacement between the members} and 4. Also a sufiicient volume of air must flow in the pick-off air stream to suppl-y the bellows device Zowith air fast enough toenable it to keep the pick-off member 2 'moving :closely in step with the member 4 while yet maintaining an adequate pressure difference. The system may thus be designed to secure close following of the primary control member 4 by the pick-off 2 so that the repeat-back movement of the member 2 is very nearly an exact measure of the movement of'theprimary control element. It should be appreciated, however, that even if these requirements are only approximately fulfilled, the apparatus will operate approximately in the manner indicated herein and will ensure good control characteristics and prevent or substantially prevent hunting of the aircraft under automatic control.

It will be immediately apparent from the foregoing description of my invention that other types of coupling or control devices, for example electrical, may be employed instead of the particular pneumatic-hydraulic coupling hereinbefore described in detail, the mechanical coupling devices having been included herein merely as an example. Thus, the above described apparatus should be viewed as exemplary of the invention only and in no way a limitation on the scope thereof.

It should be noted that the method of obtaining derivatives for control purposes according to the invention generates both the displacement, or departure, term and the derivative terms as terms present in the output of the pick-off for the primary supervising instrument. This cutputiscsually the former aipressurerditfer'ence oro an electrical voltage or current and it is therefore suitable for being led: directly Itoa ire motely situated relay-either the .servosmotorrelay or an intermediate re'lay or amplifier tor actuating the -servo-motor relay. Thus mechanical connections between the primary' supervis ing instrument and/or the pick-off associated with it on the one hand, and the relay 'it serves to control on the other hand, can 'be dispensed with. Moreover, as the restoring action :consists the applicationto the pichwil of a fierce-,rather than in'theapplicationof*a preciselydetermined movement, the d-ifiicultiesassocialted with "cable or like-mechanical restoringconnectionsgor with the use of electrical position-restoring systems for this purpose, are avoided, and it =is possible to employ simplearrangem-en-ts in the restoring connections are constituted 'by' a pair of pressure lines or by a pair ofelectrieal conduetors.

I claim:

L-Anautomatic regulating system hav-ing a movable control el'emeht and -a following elements, means for exerting a force onsaid following element dependent on the relative displacement of said elements and means connected to -Said following element for generating eounter iorces I to oppose the movement -thereo'f,said last-named means including a control spring geneilating aforce directly proportional totheamplitude of the displacement, and -means forcreating aiorce varying asthefirst' -timederi-vative of th'e d-isplacement.

2. 'An 1 automatic regulatlng' system having a movable control element and-a fol-lowingelement, means for' exertinga forceonsaid following element dependent on the rel-ative'displacement of said elements-*and'means connectedto said following element for generatingcounter forces to oppose the movement thereof, said last-named means including a controlspring generating a force 'directly proportional-totheamplitudeof the displacement, means for creating-a; force varying as the first time'derivative-of the displacement, and means for creating a force varying as the second time derivative of' the displacement.

An automatic"regulating 'systemhaving a movable control elementand a-follow-u-p element, means for exerting aforce onsaidfollow-up element dependenton a 'd-isplacementofsaid controlled element, and means connected to said follow-up element for generating counter-forces to oppose the movement thereof which include a control spring generating a, force directly proportional to the amplitude of the displacement, a dash-pot device creating a force dependent on the first time derivative of said displacement and a rotatable inertia device generating a force which is a function of the second time derivative of the said displacement.

4. An automatic regulating system as claimed in claim 3, in which said rotatable inertia device comprises a. fiy wheel, and a gear mechanism mounting said fiy wheel on said follow-up element.

5. In an automatic regulating system, a fluid pressure pick-off means including a control member, a ported housing member, the former of which is responsive to changes in a condition, and means pivotally connecting said members and enabling said former member to control the effectiVe aperture of the ports, a fluid pressure relay valve connected to the ports, a fluid pressure motor device responsive to the effective pressure supplied to the relay, means coupling said device 'to said housing to produce a restoring movement therein, yielding means mounted on said housing adapted to generate and apply a counter-force proportional to said restoring movement, and means for generating and applying a counterforce proportional to the first derivative of said movement.

6. In an automatic regulating system, a, fluid Zpressure pick-oil? means including a control member, a ported housing member, the former of which is responsive to changes in a condition, and means pivotally connecting said members and enabling said former member to control the effective aperture of the ports, a fluid pressure relay valve connected to the ports, a fluid pressure motor device responsive to the effective pressure supplied to the relay, means coupling said device to said housing to produce a restoring movement therein, yielding means mounted on said housing adapted to generate and apply a counter-force proportional to said restoring movement, means for enerating and applying a counter-force proportional to the first derivative of said movement, and means for generating and applying a counterforce proportional to the second derivative of said movement.

'7. In an automatic regulating system, a fluid pressure pick-off means including a control member, a ported housing member, the former of which is responsive to changes in a condition, and means pivotally connecting said members and enabling said former member to control the effective aperture of the ports, a fluid pressure relay valve connected to the ports, a double acting bellows device responsive to the effective pressure supplied to the relay, means coupling said device to said housing to produce a restoring movement therein, a control spring mounted on said housing adapted to generate and apply a counter-force proportional to the amplitude of the restoring movement, and means f-orgenerating and applying a counter-force proportional to the first derivative of the movement.

8. In an automatic regulating system, a fluid pressure pick-off means including a control member, a ported housing member, the former of which i is responsive to changes in a condition, and means pivotally connecting said members and enabling said former member to control the eifective aperture or the ports, a fluid pressure relay valve connected to the ports, a double acting bellows device responsive to the efiective pressure supplied to the relay, means coupling said device to said housing to produce a restoring movement therein, a control spring mounted on said housing adapted to generate and apply a counter-force proportional to the amplitude of the restoring movement, means for generating and applying a counter-force proportional to the first derivative of the movement, and means for generating and applying a counter-force proportional to the second derivative of the movement.

9. In an automatic regulating system, a fluid pressure pick-ofi means including a control member, a ported housing member, the former of which is responsive to changes in a condition, and means pivotally connecting said members and enabling said former member to control the efiective aperture of said ports, a fluid pressure relay valve connected to the ports, and a delayed action differential pressure device responsive to the efiective pressure supplied to the relay, means coupling said device to said housing to produce a restoring movement therein, control spring means mounted on said housing adapted to generate and apply a counter-force proportional to said restoring movement, a dash-pot device connected to said housing adapted to generate and apply counter-forces proportional to the first derivative of the said movement.

ROBERT HAYES NISBET,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

